1. Field of the Invention
This invention relates to a camera having means for varying the image plane size thereof and, more particularly, to a camera such as a 35 mm film camera, a video camera or the like arranged to be capable of taking shots with the size of its image plane varied through optical or electrical means to attain a spurious power varying effect, a panoramic shot effect, an effect of change-over from a full size to a half size, etc., and also to enhance photo-taking lens specifications.
2. Description of the Related Art
Some of the known 35 mm film cameras or video cameras have heretofore been provided with image plane size varying means for variously changing the image plane size through optical means, mechanical or electrical means in taking shots.
Some 35 mm film cameras, for example, have been arranged to be of the following types:
(a) A type arranged to attain an image plane size change-over effect by moving light-shielding members to partly cover the aperture of an exposure-range-defining mask on the left and right sides of the aperture in such a way as to change the image plane from a full size (36 mm.times.24 mm) over to a vertically oblong half size (17 mm.times.24 mm) and vice versa. PA1 (b) A type arranged to attain a panorama effect by moving light-shielding members to partly cover the aperture of the mask in the vertical directions of the aperture in such a way as to change the image plane from the full size over to a laterally oblong panorama size. PA1 (c) Another type arranged to attain a spurious power varying effect by changing (reducing) the image plane size in an analog manner with an aperture-diameter-varying member disposed in front of the film surface.
These cameras of the kind having the image plane size varying means are arranged to simply change the effective aperture of the mask according to the picture taking conditions by using a full size film.
Meanwhile, photo-taking lenses for use in the 35 mm film cameras or video cameras are arranged to perform a focusing action by moving either a part of or the whole of the lens along an optical axis as a shooting distance (object distance) changes. At that time, if the object distance is shorter than the nearest shootable object distance set at the time of designing, a luminous flux that would otherwise be incident on the peripheral part of the image plane is completely eclipsed by the aperture diaphragm or the edge of the photo-taking lens to hinder shooting.
In other words, the nearest shootable object distance of the camera is generally restricted by the size of the whole lens system, the size of the frontmost lens diameter or the aperture diameter of the lens.
In a case where a zoom lens is employed as the photo-taking lens, when a luminous flux otherwise would be incident on the peripheral part of the image plane with the lens in a certain zoom position on the wide-angle side of the lens, the luminous flux might be completely eclipsed by the restriction of the effective diameter of the lens. The zoom position on the wide-angle side (a wide-angle end) of the lens is thus determined partly by the restriction of the effective diameter of the lens. This tendency is salient particularly in a case where a photo-taking lens having a power varying part is used for a lens-shutter type camera.